The convergence or merging of time division multiplex-based networks—also called TDM (time division multiplexing) networks—and packet-based networks leads to new call processing requirements in terms of the conversion of signaling and user data.
In the course of the coordination of time division multiplex-based and packet-based networks with one another—the term “interworking” is also often used here—adaptations are necessary on both the subscriber side and the switching node side.
A TDM-based exchange or TDM-based switching node initiates the call control and the termination or through-connection of the user information channels. On the other hand, the range of tasks of an exchange for data transmission in the packet network—referred to in the following as a packet-oriented exchange—includes, in addition to the conventional call control, the control of the associated user information channels, which are generally routed outside the packet-based exchange, via external devices (e.g. gateways, resource servers, . . . ) which provide suitable interfaces for user data streams (e.g. using the RTP (Real Time Protocol)) and control (e.g. using one of the following protocols: MGCP (Media Gateway Control Protocol), H.248, H.323).
For the terminal device side, as well as the classical analog and ISDN terminals and private branch exchanges there are also terminals which are suitable for the packet network and permit broadband data access, but which in addition are also capable (e.g. using the H.323 protocol or the SIP (Session Initiation Protocol) protocol) of supporting the basic service features known from public telephone networks. Subscriber lines operated by means of suitable xDSL techniques (DSL: Digital Subscriber Line) or cable networks are frequently used as a broadband access medium or access network to the subscriber.
The interface between access network and transmission network, e.g. packet-based IP (Internet Protocol) network, is typically formed by means of subscriber-side adaptation facilities. The term “peripheral adapter” is also frequently used for subscriber-side adaptation facilities. Examples of subscriber-side adaptation facilities are IADs (Integrated Access Devices) for terminating a xDSL link and MTAs (Multimedia Terminal Adapters) on or in the cable modem, which terminate the access network on the transmission network side. The connection of broadband terminal equipment (e.g. PC with Internet access, television set, videophone), as well as that of traditional subscriber terminals, e.g. analog telephone, ISDN telephone, and also analog and ISDN private branch exchanges, is then possible via subscriber-side adaptation facilities and access networks.
Packet-oriented exchanges should, wherever possible, provide all the service features known from line-connected connection technology for traditional terminal devices, i.e. telephones and private branch exchanges, so that the integration of packet-oriented networks does not lead to a restriction of the range of service features offered. At the same time the non-availability of hardware and software resources and the non-accessibility of terminal devices must be detected and where applicable an alert signaled to the operator. Structures of the intermediate access networks are usually not known to the packet-oriented switching node, however. For example, failure situations affecting components and network shares which relate to the signaling path between packet-oriented switching node and subscriber terminal equipment are disclosed to the switching node only indirectly, i.e. via detection of the non-accessibility of subscribers and private branch exchanges.
Traditional analog and ISDN subscribers accessible via a packet network are identified for administrative purposes in a particular way in the packet-based switching node to distinguish them from purely packet-based subscribers (SIP, H.323) and traditional, line-connected analog and ISDN subscribers (e.g. connections via the interfaces V5.1 and V5.2). The peripheral, subscriber-side adaptation facilities possess special functions (e.g. telephony client in IADs and MTAs) which enable the transmission of the signaling information between terminal device and packet-based exchange via intermediate access networks and packet-based transmission networks or wide area networks (WANs). The packet-based switching systems and clients in the peripheral adaptation facilities (IAD, MTA) can be appropriately configured for this purpose by the network management function. From the point of view of the switching system, a distinction is made between analog and ISDN interfaces with regard to the provision of functions in the subscriber-side adaptation facilities for the transmission of the signaling information. A further differentiating feature from the viewpoint of the packet-based switching system is the assignment of service features of a main access line or a private branch exchange line. From the viewpoint of the subscriber, either an analog or ISDN terminal device operated as a main access line is then connected to the peripheral adapter (IAD, MTA), or an analog or ISDN private branch exchange (PBX) is connected in the same way.
With regard to ISDN interfaces, e.g. on the peripheral adaptation facility, a distinction is made between two different access types or interfaces.
With the basic access, also referred to as BRA (Basic Rate Access), one or two user information channels are present. Often there are two user information channels (B channels), each operating at 64 kbit/s (56 kbit/s in the USA), and a signaling channel (D channel) operating at 16 kbit/s.
The second access type, also referred to as PRA (Primary Rate Access), is the primary rate TDM access, usually consisting of 30 B channels (on account of the PCM30 system), a synchronization channel, and a signaling channel (D channel). In accordance with standardization, up to 4 PCM30 systems with a single D channel can likewise be combined into a PRA.
Contrary to the case of a packet-based exchange, the status (Layer 1, Layer 2, blocking state) of the ISDN access (BRA, PRA) is known to a traditional local exchange of a TDM network owing to physical line termination or the interface protocols to subscriber concentrators and access networks.
Small ISDN private branch exchanges must also be connectable for packet networks via a BRA or a plurality of BRAs by means of peripheral adapters; large ISDN private branch exchanges must be connectable via one or more PRAs, whereby it must also be possible to support mixes of BRAs and PRAs with regard to a given ISDN private branch exchange. In this case BRA and PRA are possibly connected and physically terminated via a standardized peripheral adapter or via specific peripheral adapters. The ISDN signaling can then be exchanged between peripheral adapter and packet-oriented exchange using packet-based means (e.g. by means of ISDN User Adaptation IUA and SCTP). This typically takes place by means of the DSS1 (Digital Signaling System No. 1) protocol, details of which are specified in the ITU-T Q.931 standard (ISDN user-network interface layer 3 specification for basic call control).
The object of the invention is to ensure flexible and efficient handling of different ISDN access types by a packet-oriented exchange.
The object is achieved by a method, a peripheral device and a packet-oriented exchange according to the independent claims.
In general, an exchange comprises peripheral units, e.g. access units for subscribers or lines, as well as central units or a central component or core which includes, for example, a central computer platform, a message buffer, a switching matrix, protocol termination facilities, background memory, etc. With regard to a packet-based exchange the existence of a switching network is optical in this arrangement. According to the invention an adaptation is performed in a peripheral unit, by means of which adaptation the different ISDN accesses can be represented and controlled in the central core of the packet-oriented exchange in the same uniform manner. A peripheral unit in which the adaptation according to the invention can be performed is the packet control unit of a packet-oriented exchange which controls the user data transmission over the packet network.
In the context of the method according to the invention, signaling information is exchanged between an ISDN access, for example an ISDN BRA or ISND PRA access, and the central core of a packet-oriented exchange via a peripheral unit of the packet-oriented exchange. An ISDN terminal device or an ISDN private branch exchange, for example, can be connected to the ISDN access. The handling or processing of the signaling information transmitted by the ISDN access takes place in the central core of the packet-based exchange independently of the type of the ISDN access. For example, no distinction is made between ISDN BRA and ISDN PRA accesses in the packet-based exchange. For the purpose of ISDN access type-independent handling of signaling information by the central core of the packet-oriented exchange, signaling information transmitted from the ISDN access to the exchange is adapted in suitable peripheral units of the exchange. Similarly, signaling information transmitted by the central core of the packet-oriented exchange in the direction of the ISDN access is adapted in suitable peripheral units of the exchange in accordance with the ISDN access type. In this way different ISDN accesses can be represented by a single access type in the central core of the packet-oriented exchange. Different ISDN access types generally comprise a different number of user data channels. Thus, the PRA access generally has 30 user data channels and one signaling channel. The BRA access or basic rate access, on the other hand, comprises one or two user data channels and one signaling channel. In the inventive adaptation of signaling information in the peripheral unit, the different user data channels can be mapped onto one another for different access types. In this case user data channels or logical ports in the packet network can be distinguished by the addressing of the packets or the addresses of the packets. In the context of user data transmission in the TDM and in the packet network, the term “bearer” is also often used instead of the term “user data channel”. According to the invention, an assignment then exists between logical port or user data channel (bearer( and the provisioning of resources in packet-oriented switching systems. For example, a call processing program can be executed in the packet-oriented switching system in accordance with the logical port or the user data channel. On the ISDN access side, physical ports are provided and also user data channels which are assigned to fixed time slots during the transmission via a TDM network. The signaling information relating to the ISDN access and transmitted to the packet-oriented exchange is often adapted in a peripheral adapter (e.g. IAD or MTA) for transmission to the packet-oriented exchange via a packet network. The signaling information arriving at the peripheral unit is adapted for example with the aid of a table for ISDN access type-independent processing by the central core of the packet-oriented exchange. Such a table can be set up in the peripheral unit by the network management. This is conditional upon the network management knowing the hardware interfaces or the physical ports of the ISDN access in order to be able to set up the table. In contrast to the network management, the details regarding the ISDN access are transparent to the central core of the packet-oriented exchange. The provision of the means for adaptive signaling information transmitted from an ISDN access to the central core of the packet-oriented exchange for the purpose of ISDN access type-independent processing and handling of the signaling information by the central core of the packet-based exchange in a peripheral unit is flexible with regard to changes and configurations. A costly and complex implementation of means for differentiating different ISDN access types in the central core of the packet-oriented exchange is avoided, i.e. the implementation overhead is reduced. This also simplifies the expansion of traditional exchanges by control functions for voice connections routed via a packet network. The inventive adaptation in the peripheral unit also permits a concentration of user data channels. For example, the 30 user data channels of a private branch exchange with PRA access can be mapped to fewer than 15 BRA accesses in the packet-oriented exchange. In this case it is assumed that the previously mentioned logical port type of the packet-based exchange coincides with the ISDN BRA with up to two bearer channels. This is an economical solution when there is only low utilization of the user data channels of the ISDN access. By configuration of the peripheral unit the concentration of the user data channels can be flexibly adjusted as necessary to a change in the utilization of the user data channels of the ISDN access. The inclusion of PRA with more than 30 user information channels is likewise possible in this case.
When there are differences between the logical ISDN accesses in the packet-oriented exchange and the subscriber-side physical ISDN accesses, in addition to a mapping of the user data channel references, e.g. channel numbers, the call ID often has to be adapted also. In this context the call ID denotes the identification information referred to as the “Call Reference” in ITU-T Q.931, ISDN user-network interface layer 3 specification for basic call control. This call reference serves to distinguish calls. In contrast to the call number for a subscriber, the call reference for a connection can assume different values on disjunct line sections. Call references are assigned to connections. After the end of a connection the associated call reference is free again and can be reassigned. Finally, a call reference is only unique within a signaling channel. The latter attribute means that it is necessary for the call reference to be converted in many cases. For example, logical BRA ISDN accesses are used on the exchange side, each of which comprises two basic channels and a signaling channel. A number of these logical BRA ISDN accesses are then mapped to one PRA ISDN access with thirty user data channels and one signaling channel. Consequently, multiple signaling channels are mapped to one signaling channel; in other words, without the call references being adapted, the uniqueness of the call references would be open to question.
Signaling information sent from the ISDN access to the packet-oriented exchange can be transmitted via a peripheral adaptation function in the packet control unit of the packet-based exchange, said function being responsible for adaptations for transmission of the signaling information via a packet network. The D channel protocol DSS1 (Digital Subscriber Signaling System No. 1) is used, for example, for the signaling between ISDN access and peripheral adaptation function of the packet control unit. In this case the packet control unit is a special peripheral unit of the packet-based exchange.